EDIT: Looks like jah003 has the same problem I used to have. Here is how to solve it for ROKU:
Some tips in case others have trouble viewing SECN+ and other ESPN content through the app that you should have access to. I used to always run into this with ESPN app on ROKU devices. What I found was it has something to do with the automatic authentication through my cable / internet provider (Xfinity/Comcast). Even though I have access through my subscription, it would tell me "Media Not Allowed" or "Not authorized to view this content" for SECN+ stuff that I just viewed no problem a few days before. Like others have said, it would be a 10 minute ordeal logging in / out / unisntalling the app, etc. and nothing would work. Here is how I got it to work:
1. When authenticating via ESPN.com\activate, your Roku gives you a code to enter, then my Xfinity credentials always automatically authenticated from my phone. Even though it says success, it won't work. You have to remove the credentials from iPhone settings > Tv Provider then do private web browsing option on Safari, THEN go to ESPN.com/activate, enter the code from your Roku, then it should not automatically authenticate. Enter username and password for your TV provider then it works.
2. Sometimes this trick would still not work and I found it is because I was on my home wifi, which it would sometime automatically authenticate, because I have Xfinity Wi-Fi and Xfinity cable so it would sometimes automatically authenticate. You have to fake it out by logging in just through cellular Internet.
My theory is this happens to a lot of people with the ESPN app, it is not just limited to ROKU because the ESPN app authentication uses some kind of Adobe technology to pass the credentials and somehow those are expiring and getting stuck. A fresh login session does not help for some reason, so have to fake it out.